This invention relates to an operating mechanism for a four-pole electrical breaking apparatus, namely, a four pole circuit breaker having the first three poles associated with the three phases of an electrical supply system and the fourth pole being associated with the neutral.
Generally, four pole circuit breakers are usually derived from a three pole design. Accordingly, the mechanism for controlling the opening, closing and resetting of the circuit breaker is, in the case with a three pole design, associated with the center pole. In such a design, the operating mechanism is positioned over the center pole and, accordingly, the force of the mechanism is applied on either side of the center pole. This design allows the forces from the mechanism to be distributed symmetrically on either side of the center pole.
However, as a fourth pole is added to such a configuration, the forces are no longer distributed symmetrically. This asymmetry gives rise to problems of unbalanced loading at the fourth pole. This unbalanced loading is caused by the flexing or bending of the crossbar, which is magnified at the fourth pole. This bending and/or flexing will contribute to a loss of motion, and accordingly, a lower contact pressure being applied by the crossbar at the pole furthest from the mechanical mechanism.
U.S. Pat. No. 4,383,146 and 5,357,066 both offer a proposed solution to the above-mentioned problems. However, both patents require significant modifications to the controlling mechanism, including the incorporation of a secondary mechanism, as well as modifications to the fourth pole.